Light emitting diodes (LEDs) emit light when charged with electricity. LEDs provide light in a wide array of electronic devices. Often, LEDs are incorporated into display devices for presenting alphanumeric information or icons. Typically, LEDs are manufactured into an electronic chip (e.g., LED chips) that provide for easy integration into electronic devices. LED display devices may by integrated into electronic devices, such as digital read-out displays, by soldering the leads of an LED display device to a circuit board.
A typical LED display device includes an overlay that is used to present the specific information. An overlay includes a transparent portion that is placed over an LED, such that a lit LED can be seen through the transparent portion. For example, the transparent portion may be in the shape of an icon. Overlays are typically manufactured using plastic, and are typically approximately 0.5 mm in thickness.
As described above, an LED display device is integrated into electronic devices by soldering the LED device to a board using solder paste. Previously, the solder paste used was an alloy including tin and lead. Such solder paste has a melting point of approximately 182 degrees Celsius and is typically reflowed at a temperature of 240 degrees Celsius.
Environmental and health concerns have increased the use of environmental friendly processes in the manufacturing industry. One of the proposed changes is eliminating the use of lead-based products. Currently, solder paste has been changed to remove the lead content. However, lead-free solder paste needs a higher temperature profile during the solder reflow process. Typically, a temperature of at least 260 degrees Celsius is needed. Current display overlays are not able to withstand these higher temperatures, causing the overlay to shrink substantially, resulting in warpage. This shrinkage is unacceptable as it is a major product defect.